Field of the Invention
The present invention relates to a foreign substance detection method, a foreign substance detection apparatus, an exposure method, and a method of manufacturing a device.
Description of the Related Art
The mainstream of recent semiconductor exposure apparatuses is a scanning exposure apparatus which exposes a substrate by relatively scanning the substrate and an original while irradiating a region smaller than a region to be exposed on the substrate with light. A scanning exposure apparatus generally has a focus detection system arranged before or after an exposure region to detect the height position of a substrate immediately before exposure. The apparatus controls a substrate stage to match the height of the substrate with the focal position of a projection optical system. In this case, the focus measurement value detected by the focus detection system tends to have a gradual trend in a normal process. When a steep change is observed in a focus measurement value, it often indicates that there is a foreign substance on a substrate or a foreign substance has adhered to a member (chuck) which chucks and holds the substrate. Extreme caution is given to foreign substances on the chuck, in particular, in a semiconductor manufacturing site, in which the chuck is periodically cleaned or replaced with a new one.
Japanese Patent Laid-Open No. 2006-140459 discloses the use of an immersion exposure apparatus to meet a requirement for further micropatterning of semiconductor devices. The immersion exposure apparatus disclosed in Japanese Patent Laid-Open No. 2006-140459 exposes a substrate while the air gap between at least partial region of the final surface of a projection optical system and a substrate on a substrate stage is filled with a liquid. The immersion exposure apparatus disclosed in Japanese Patent Laid-Open No. 2006-140459 has a detector provided on the substrate stage to detect foreign substances lower in specific gravity than the liquid or air bubbles existing in the liquid between the final surface of the projection optical system and the substrate by using an image sensor.
Japanese Patent Laid-Open No. 2008-140814 discloses a technique of judging the presence/absence of a foreign substance based on a detection result from a focus detection system which detects the height position of a substrate.
However, the immersion exposure apparatus disclosed in Japanese Patent Laid-Open No. 2006-140459 needs to be equipped with a dedicated detector including an image sensor for detecting foreign substances. In addition, in the exposure apparatus disclosed in Japanese Patent Laid-Open No. 2008-140814, the focus detection system performs measurement while a substrate is chucked on the chuck, and hence it is difficult to judge whether a foreign substance exists on the substrate or chuck. For this reason, the exposure apparatus disclosed in Japanese Patent Laid-Open No. 2008-140814 requires maintenance including the cleaning of the chuck every time a focus abnormal value is detected. This prolongs the maintenance time for the apparatus and affects productivity. For example, the chip production yield decreases.